GaN-based Resonator Shows Promise For 5G
Highly sensitive GaN-based MEMS oscillator operates stably even at high temperatures
Liwen Sang, a scientist at the International Center for Materials Nanoarchitectonics, National Institute for Materials Science in Japan has developed a MEMS resonator that operates stably even under high temperatures by regulating the strain caused by the heat from GaN. The result were presented at the IEEE International Electron Devices Meeting (IEDM2020) in December.
High-precision synchronisation is required for 5G with a high speed and large capacity. To that end, a high-performance frequency reference oscillator which can balance the temporal stability and temporal resolution is necessary as a timing device to generate signals on a fixed cycle.
Conventional quartz resonators have poor integration capability and their application is limited. Although MEMS resonator can achieve a high temporal resolution with small phase noise and superior integration capability, silicon-based MEMS resonators suffer from a bad stability at higher temperatures.
In the present study, a high-quality GaN epitaxial film was fabricated on a Si substrate using MOCVD to fabricate the GaN resonator. The strain engineering was proposed to improve the temporal performance. The strain was achieved through using the lattice mismatch and thermal mismatch between GaN and Si substrate. Therefore, GaN was directly grown on Si without any strain-removal layer.
By optimising the temperature decrease method during MOCVD growth, there was no crack observed on GaN and its crystalline quality is comparable to that obtained by the conventional method of using a superlattice strain-removal layer.
The GaN-based MEMS resonator was verified to operate stably even at 600K. It showed a high temporal resolution and good temporal stability with little frequency shift when the temperature was increased. This is because the internal thermal strain compensated the frequency shift and reduce the energy dissipation. Since the device is small, highly sensitive and can be integrated with CMOS technology, it is promising for the application to 5G communication, IoT timing device, on-vehicle applications, and advanced driver assistance systems.
The research was supported by JST's Strategic Basic Research Program, Precursory Research for Embryonic Science and Technology(PRESTO). This result was presented at the IEEE International Electron Devices Meeting (IEDM2020) held online on December 12-18, 2020, titled 'Self-Temperature-Compensated GaN MEMS Resonators through Strain Engineering up to 600 K.'